Tribological properties of aqueous solutions of alkyl polyglucosides

This research was inspired by increasing interest in ecological lubricants. Aqueous solutions of alkyl polyglucosides (APGs) were chosen as potential lubricant compositions. Commercially provided products were tested for surface tension, wetting angle, light diffusion and viscosity. Additionally, atomic force microscopy, polarized light microscopy and X-ray spectroscopy were employed. The tests were supposed to identify micellar and liquid-crystalline structures formed in bulk and surface phases. The tribological tests were performed with a four-ball machine and with a ring-on-disc apparatus. The friction couples were made of steel. On the basis of the results obtained via four-ball machine tests, the influence of additive concentration on friction coefficient (μ), wear and seizure load was assessed. As compared to water, the friction coefficient was reduced even seven times and the seizure twice. Also anti-seizure properties significantly changed. For instance, for some of the compositions applied, seizure did not occur, even at a maximum load of 8 kN. The dependence of tribological quantities on concentration was not monotonic. One can note, however, a reduction of μ and wear and a significant improvement of anti-seizure properties, at concentrations of about 0.1%. The influence of the additive applied on the friction coefficient was similar for the ring-on-disc test. The changes in the tribological properties observed could be explained by high APG affinity to the surface, while the effect of concentration on the tribological performance is caused by changing the solution structure. The compounds applied can form various types of micelles and mesophases in bulk and surface phases.